| 2205duplex stainless steel is a kind of steel which has good mechanical property andcorrosion resistance property. Until now, there are still some problems in the weldingprocessing between2205duplex stainless steel and Q345R high strength low alloy steel,especially mechanism in the change of microstructure and properties during welding. In thisstudy, two kinds of welding methods, including shielded metal arc welding and gas tungstenarc welding were utilized. Also three kinds of welding alloy, including2209,309and309Mo,were employed to joint2205duplex stainless steel and Q345R steel. After welding, themicrostructure, mechanical properties and corrosion resistance properties of welded jointswere investigated. All of these were done to supply scientific basis for dissimilar steelswelding between2205duplex stainless steel and other steels.Thermal cycle of special location during welding was studied by ANSYS finite elementanalysis software. The microstructure of welded joints was observed. Tensile property, bendproperty, micro hardness and corrosion resistance property were tested. Moreover, the changeof microstructure and micro hardness during aging treatment was investigated. The micro&nano mechanical properties of micro location in welded joints were also studied.Following conclusions can be drawn from tests and analysis in this study.Results of finite element analysis show that there is a longest time of1225s in thebottom of fusion zone from weld metal to Q345R base metal when the temperature is below250℃. However, the time of top fusion zone from weld metal to Q345R base metal is only1066s and is the shortest. The place located in the middle layer of fusion zone from weldmetal to Q345R has a medium time of1148s when the temperature is below250℃. Thetime below700℃of gas tungsten arc welding metal is311s longer than that of top shieldedmetal arc welding metal which is211s.The base metal, heat affect zone of2205duplex stainless steel and weld metals are allconstituted by duplex microstructure of austenite phase and ferrite phase. The ratio andmorphology of phase are all influenced by thermal cycle and alloying element. The carbonmigration area, which located at the interface from weld metal to Q345R steel base metal, isaffected by thermal cycle and alloying element. Ferrite phase fraction is influenced by ratio ofChrome equivalent and Nickel equivalent and is positive proportional to the ratio of Chromeequivalent and Nickel equivalent. Because of the heating time higher than700℃of shieldedmetal arc welding is shorter, ferrite phase fraction of shielded metal arc welding is higher thanthat of gas tungsten arc welding. When the shielded metal arc welding is applied, massfraction of Nickel in E2209weld metal is higher than that in E309and E309Mo. Because of the refining effect of Nickel element, the microstructure of E2209fusion zone is finer thanthat of E309and E309Mo. Carbon migration degree is negative proportional to mass fractionof Mo and is positive proportional to heat time.The tensile and bend properties of welded joints can all meet the operating requirement.The tensile strengths of all joints are higher than that of Q345R steel base metal. The tensilefracture is dimple and locates at Q345R steel base metal. Moreover, there is no crack duringface bending and reserve bending. All of these show that there is good plasticity of all joints.The hardness from Q345R steel based metal to weld metal, and to2205duplex stainless steelis nearly increased. There is a fluctuation in micro hardness which is decreased firstly, thenincreased and decreased again, at the interface from Q345R steel to weld metal. The degree offluctuation is affected by heating time, and is positive proportional to the heating time.Corrosion resistance property of E2209weld metal is comparable to that of2205duplexstainless steel. Corrosion potential tested in3.5wt.%NaCl solution of E2209weld metal is-0.519V higher than that of2205duplex stainless steel which is-0.521V. Moreover,intergranular corrosion rate of E2209weld metal is0.4082g.m-2.h-1higher than that of2205duplex stainless steel which is0.4006g.m-2.h-1. The investigate results show that theintergranular corrosion products are ferrite.When butt joints are aged at high temperature, ferrite phase in2205duplex stainless steeland weld metal transformed into austenite phase continually, and accompany with theprecipitation of σ phase. The hardness of joints is changed greatly. Precipitation of σ phase isinfluenced by aging temperature, aging time and alloying element. Ferrite phase transformsinto austenite phase gradually at700℃. Ferrite phase, austenite phase and σ phase coexist at900℃. Fraction of σ phase in weld metal after aging is positive proportional to mass fractionof Molybdenum. σ phase is intermetallic compound of Iron and Chrome, and the massfraction of Chrome is33.5%. Improvement in hardness of2205duplex stainless steel andweld metal aged at900℃is greater than that aged at700℃. When using same weldingalloy, hardness of shielded metal arc weld metal aged at900℃is higher than that aged at700℃. When using same welding method, hardness of E2209weld metal is higher than thatof E309and E309Mo. Hardness of Q345R is lower than weld metal, which decreased firstlyand increased lastly with aging time extended.Results of finite element analysis show that Meyer exponent increases when the workinghardening exponent increases. Average Meyer exponent of gas tungsten arc weld metal isminimum. Meyer exponent of2205duplex stainless steel base metal is maximum, whichhigher than that of gas tungsten arc weld metal and shielded metal arc weld metal. Thisindicates that plasticity of tungsten arc weld metal is the best, then is shielded metal arc weld metal, and the2205duplex stainless steel is the worst. When only one kind of weldingmethod is employed, Meyer exponent of309weld metal is the minimum. This illustrates that309weld metal owes the best plasticity. Hardness of ferrite phase is346.83HV, higher thanthat of austenite phase which is261.62HV. Steady creep stress exponent of ferrite phase is82.79much higher than that of austenite phase which is36.26. This indicates that creepresistance of ferrite phase is greater than that of austenite phase. The hardness of σ phase is1764.8HV much higher than that of ferrite and austenite phase. This illustrates that σ phase isa kind of hard and brittle phase. |
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